The trigger is found within the capture buffer (there is no hardware trigger circuit), so as BenF says in the following quote, reducing the capture buffer size (depth) could increase the refresh rate by a factor of 10 which would improve the viewing of non-repeating waveforms in this T/Div range. What you are wanting would require some form of hardware trigger and the Nano does not have that. A fast scan mode would simply have the waveform jumping all around on the screen x-axis.
I really hope that you are considering this option in a future release.